All right… but, oh, sorry, you do not know what a “1-2-3 counter” is ?! Well that is the name I found for it, please propose a better one !
THE tricky thing when using lights with batteries is to be sure you do not run out of battery during a ride, without also charging them every other day, just to make sure & in case. So I figured out from the specs of the front and rear lights I am using that I can use them for 3 round-trip rides, i.e. ca. 3h30. So, each time I start a ride, a move the red piece of wood from that counter from one position to the next, in order to always know how many rides I made with my charged batteries. So, when returning home with a “3″, I know this is time to charge !
My son [quite young at that time !] painted the numbers and put the colors.